Method of separating hydrocarbons from a sample



Feb. 7, 1967 D. M AULIFFE 3,303,002

METHOD OF SEPARATING HYDROCARBONS FROM A SAMPLE Filed Sept. 24, 1963 AMPLIFIER ELECTROMETER FIG.1

INVENTOR CLAYTON D.McAUL/FFE United States Patent 3,303,002 METHOD OF SEPARATING HYDROCARBONS FROM A SAMPLE Clayton D. McAulitfe, Fullerton, Califi, assignor to Chevron Research Company, a corporation of Delaware Filed Sept. 24, 1963, Ser. No. 311,072 6 Claims. c1. 23-230 This invention relates to geochemical methods of prospecting for subterranean hydrocarbon deposits and more particularly this invention relates to improved methods and apparatus for separating minute quantities of hydrocarbons from samples so that the hydrocarbons may be quantitatively analyzed for the presence of selected hydrocarbons.

In copending application Serial No. 174,172, filed February 19, 1962, and now abandoned, a method of geochemical prospecting for petrolifero-us deposits is set forth. In practicing that method it has been found that special methods and apparatus are necessary to achieve separation of the hydrocarbon constituents of the samples collected in accordance with that invention. More precisely, it has been found that special precautions must be taken to prevent contamination of the hydrocarbon samples with the hydrocarbons contained in the atmosphere in which the hydrocarbon separation is accomplished. This is especially true with regard to the lighter hydrocarbons, i.e., methane and ethane, components of the sample. Further, unless special precautions are observed in the separation operation, loss of the lighter hydrocarbons from the sample is likely to occur. Since the hydrocarbons are present in the samples in very small quantities and are measured in parts per billion, it is obvious that it takes only a small loss or contamination to seriously impair the reliability of a sample. If contamination by background hydrocarbons or loss of light hydrocarbon constituents occur during the separation procedure then the samples give an unreliable count and resampling must be done. Since the samples are collected from widely spaced-apart locations of the earth, it is necessarily a time-consuming and expensive operation and therefore must be avoided if at all possible.

It is therefore a particular object of the present invention to provide an improved method and apparatus for separating the hydrocarbon constituents from samples.

In a broad aspect the method of the present invention comprises the steps of establishing a vacuum in a chamber, flowing a sample suspected of containing trace amounts of hydrocarbons into the chamber to dissolve out the gaseous constituents of the sample from the chamber, and collecting a portion of the said gaseous constituents to test for selected hydrocarbons.

Further objects and advantages of the present invention will be apparent from the following detailed description read in light of the accompanying drawing which is a part of this specification and in which:

FIGURE 1 is a view illustrating apparatus assembled in accordance with the preferred embodiment of the invention;

FIGURE 1A is a view illustrating an alternative arrangement of apparatus assembled in accordance with the invention;

FIGURE 2 is a view illustrating an arrangement of apparatus for quantitatively determining the presence of selected hydrocarbons in the gases separated from a sample in accordance with the invention.

Refer now to the drawings and to FIGURE 1 in particular where apparatus assembled in accordance with the invention is illustrated. A sample container which is preferably a sample collection bottle 20 is connected to a source of nitrogen gas (not shown) by means of 3,303,002 Patented Feb. 7, 1967 tubing 21. A valve 22 controls the flow of gas through the tubing 21. A tube 23 is provided to drain the collection bottle 20. An appropriate stopper 26 is placed in the top of bottle 20 so that all flow in and out of the bottle must be through tubing 21 and tubing 23.

The top of a vacuum chamber 25 is connected to tubing 23 by means of tubing 29 and flexible hose 28. An O-ring 12 seals the connection between tube 29 and chamber 25. A valve 24 on tube 29 controls fl-ow from the sample bottle 20 to chamber 25. The vacuum chamber 25 has a greater valume than the sample bottle 20. An exit port in the top of vacuum chamber 25 is connected to a pump 33 by suitable means such as tubing 21, O-ring 14, valve 30, and tubing 32. The pump is of a suitable size to evacuate the vacuum chamber and to provide a vacuum of less than 0.1 mm. of mercury.

A source of nitrogen gas 34 is connected to the exit port in the vacuum chamber 25 by means of tubes 35, 31 and 29. Valve 36 and pressure reducing regulator 37 control the flow of the gas into the vacuum system.

A compression chamber 39 is connected to the exit port in the vacuum chamber by means of tubing 31. Valve 38 controls flow in tubing 31. Suitable means are provided for increasing the pressure in chamber 39. For example, :a mercury-filled leveling bulb 50 is connected by flexible tube 51 to the bottom of chamber 39. A valve 52 controls the flow of mercury into and out of chamber 39. Thus when valve 52 is opened and the bulb 50 is raised to the position shown in phantom, mercury will flow in chamber 39 and slightly compress the gas contained therein.

The upper end of chamber 39 is connected to Y-shaped tube 61. One branch of tube 61 leads through valve 56 to tube 55 to a mercury manometer (not shown). The other branch of tube 61 is connected through valve 57 and tube 58 to a hypodermic syringe fitting 59. A suitable hypodermic syringe 60 is insertable into fitting 59 to remove contents of tube 39 after compression by mercury.

An alternative arrangement of apparatus useful with sediment samples rather than water or liquid samples is illustrated in FIGURE 1A and will be discussed briefly. The sample, which might be drilling chips or drilling mud, is contained in sample container 40. A source of water (not shown) is connected to the sample chamber by suitable means such as tube 41. A valve 42 controls the flow of water into sample container 40. An outlet 43 from the sample container is connected to the vacuum chamber 25 illustrated in full in FIGURE 1, by means of appropriate flexible tubing 45. A pinch clamp 44 controls flow through tubing 45.

The procedural steps of the present method are similar when used to separate trace hydrocarbons from either drilling chips or the like, or liquid samples. With reference again to the apparatus of FIGURE 1, the method of the present invention will be described in greater detail. In operation the bottle 20 containing the sample is connected by suitable tubing to the vacuum chamber 25 and the valve 24 between is closed. Tubing 23 is filled with sample Water up to valve 24. The system downstream from valve 24 is then flushed by the following procedure to remove contaminants. Valves 36, 52, and 57 are closed and valves 30, 38 and 56 are opened. Pump 33 removes air from the vacuum chamber 25, the compression chamber 39 and the intervening tubing. When the pressure measured at the manometer is less than 1 mm. mercury, valve 30 is closed. Nitrogen gas is then admitted to the system by opening valve 36. The nitrogen is then pumped off by means of pump 33 after again opening valve 30 and closing valve 36. The prefl-ush as described above is preferably repeated. The preflush completely removes from the vacuum chamber any gas which might contain hydrocarbons and which if not removed could serve to contaminate the sample being tested.

After the flushing of the system has been accomplished, pump 33 is run until a vacuum of at least 1 mm. and preferably at least 0.1 mm. of mercury is obtained on the manometer. Then valves 56 and 30 are closed.

The valve 24 between the sample bottle 20 and the vacuum chamber 25 is now opened to admit the water sample to the vacuum chamber. The valve 24 is adjustable so that the rate of flow of the sample into the vacuum chamber 25 can be varied. The rate of flow of the sample into the chamber should be adjusted within limits. A range of flow such that a /2 gall-on sample enters the sample chamber in between 2 and 10 minutes has been found most suitable. It is most desirable to adjust the flow so that a /2 gallon sample flows into the chamber in about minutes. As the water enters the vacuum chamber 25 the gases, principally nitrogen or nitrogen and oxygen and any light hydrocarbons dissolved in the water break out from the water and go into the gas phase. When the sample has been displaced into the vacuum chamber the valve 24 between the sample bottle 20 and the vacuum chamber 25 is close-d. The volume remaining in the vacuum chamber, the compression chamber, and associated tubing over the water sample in the vacuum chamber is approximately equally divided on either side of valve 38. The quantity of gas evolved from the water will normally be about of the unfilled volume of the system so that the gas is still at about one-tenth atmospheric pressure.

Valve 38 between the vacuum chamber 25 and the compression chamber is now closed. Valve 52 is opened to :permit mercury to enter the bottom of the compression chamber. The leveling bulb 50 is raised to the position shown in phantom in FIGURE 1 to compress the gas in chamber 39 to slightly above atmospheric pressure. A hypodermic syringe 60 is inserted into fitting 59 and valve 57 is opened. The gas is collected and measured in the syringe.

When the sample is drilling fluid and cuttings, as illustrated in FIGURE 1A, the procedure differs slightly in that the sample is drawn from container 40 into vacuum chamber 25 and followed and rinsed by hydrocarbonfree water entering through tubing 41. Sufficient hydrocarbon-free water is added to bring the volume in vacuum chamber 25 to a predetermined amount which leaves an appropriate air space in the chamber. Pinch clamp 44 is closed at the appropriate time to provide the desired volume of liquid in vacuum chamber 25.

The hydrocarbons separated from water or drilling fluid samples by the above-described procedures contain from 1 through at least 8 carbon atoms. The gas separated by the above procedures and collected in the syringe is then injected into suitable apparatus for analysis for hydrocarbon components. For example, with reference to FIGURE 2, a chromatographic column with a hydrogen-flame ionization detector may be used to quantitatively examine for the presence of hydrocarbons having from 1 through 8 carbon atoms. The gas is injected from syringe 60 into injection port 64 and chromatographic column 61. The rate of flow of the various components of the gas through the column vary so that individual hydrocarbon components will emerge at the.

hydrogen-flame ionization detector 62. There the quantity of the individual hydrocarbon components is measured and transmitted to a recorder chart 63 for visual reading of the quantitative measurement.

Although only a few embodiments of apparatus have been illustrated and described herein, the invention is not to be limited to those embodiments but rather only by the scope of the appended claims.

I claim:

1. In -a method of geochemical prospecting wherein samples are collected and the hydrocarbon content of said samples is determined and recorded to give an indication of the possible whereabouts of valuable petroleum deposits, the improvement in separating at least the hydrocarbons containing from 1 to 8 carbon atoms from each sample comprising the steps of establishing a vacuum of at least 0.1 mm. mercury in a chamber,

7 closing said chamber, flowing only :a liquid sample into the vacuum in said chamber at a rate equivalent to /2 gallon in from 2 to 10 minutes whereby the vacuum causes gas including any hydrocarbon constituents thereof to come out of said sample, collecting at least a portion of said gas, analyzing said gas for the hydrocarbon constituents thereof and repeating the above steps for each of the remaining samples.

2. In a method of geochemical prospecting wherein samples are collected and the hydrocarbon content of said samples is determined and recorded to give an indication of the possible whereabouts of valuable petroleum deposits, the improvement in separating at least the hydrocarbons containing from 1 to 8 carbon atoms from the sample comprising the steps of establishing a vacuum of at least 1.0 mm. mercury in a closed chamber, flowing only a stream of a liquid sample into the vacuum in said chamber at a rate equivalent to /2 gallon in from 2 to 10 minutes whereby the vacuum causes gas including any hydrocarbon constituents thereof to break out of said sample, compressing said gas and collecting at least a portion of said gas for analysis for the hydrocarbon constituents thereof.

3. The method of claim 2 where the said sample is composed of drilling chips and water is flowed through said chips and forms the stream of said sample,

4. The method of claim 2 where the sample is drilling mud and water is flowed through said mud and forms the stream of said sample.

5. The method of claim 2 where the closed chamber is preflushed with an inert gas prior to establishing the vacuum therein.

References Cited by the Examiner UNiTED STATES PATENTS 2,514,690 7/1950 Bliss et a1. 23-230 2,923,151 2/1960 Engle et al 55204 3,118,738 1/1964 Ja mieson .a 23-230 3,208,826 9/1965 Arnett 23-230 REUBEN FRIEDMAN, Primary Examiner.

B. NOZICK, C. N. HART, Assistant Examiners. 

1. IN A METHOD OF GEOCHEMICAL PROSPECTING WHEREIN SAMPLES ARE COLLECTED AND THE HYDROCARBON CONTENT OF SAID SAMPLES IS DETERMINED AND RECORDED TO GIV E AN INDICATION OF THE POSSIBLE WHEREABOUTS OF VALUABLE PETROLEUM DEPOSITS, THE IMPROVEMENT IN SEPARATING AT LEST THE HYDROCARBONS CONTAINING FROM 1 TO 8 CARBON ATOMS FROM EACH SAMPLE COMPRISING THE STEPS OF ESTABLISHING A VACUUM OF AT LEAST 0.1 MM. MERCURY IN A CHAMBER, CLOSING SAID CHAMBER, FLOWING ONLY A LIQUID SAMPLE INTO THE VACUUM IN SAID CHAMBER AT A RATE EQUIVALENT TO 1/2 GALLON IN FROM 2 TO 10 MINUTES WHEREBY THE VACUUM CAUSES GAS INCLUDING ANY HYDROCARBON CONSTITUENTS THEREOF TO COME OUT OF SAID SAMPLE, COLLECTING AT LEAST A PORTION OF SAID GAS, ANALYZING SAID GAS FOR THE HYDROCARBON CONSTITUENTS THEREOF AND REPEATING THE ABOVE STEPS FOR EACH OF THE EMAINING SAMPLES. 